Mr Marshall said police spent some time secretly tracking the gang's movements before raiding Mercer's haulage company nearly six months ago.

He said all five defendants were arrested at the scene although two other men - Anthony Fraser and Neil Mulligan - who were also allegedly involved "did a runner".

The barrister said a search of the premises uncovered 1.4 tonnes of cannabis in Mercer's warehouse "waiting for the customers".

A further 882lb (400kg) were recovered from Soutter's van, while 132lb (60kg) of the more potent "skunk" form of the drug was allegedly found in Rowe's Volvo Estate.

"That is all worth an awful lot of money, certainly millions of pounds," counsel explained.

"Even this importation alone ranks as a major one, but when you look back and see how many have gone in previously you can see really quite massive quantities of cannabis resin have been brought into the country in this way.

"It is really a significant drug smuggling enterprise."

Mr Marshall told jurors that of the two on trial only Mercer answered questions when interviewed.

The haulage company boss told officers he had been approached three weeks earlier by someone he knew only as Tony for the use of his yard for a "loading and unloading" exercise.

He maintained that after being offered £500 for his trouble, he asked if there was anything "iffy" going on, but was assured everything was above board.